Raising lots of axolotl is easy, selling them is the issue. With 500 to sell you need to look for several customer types. Private sales which generate the most revenue but will have a low uptake, direct sales to retail outlets which will take a higher volume at a lower rate and wholesalers who will take large volumes at a fraction of the retail value. I suggest you start sourcing buyers now as work and costs spiral fast with this amount of axys. Many people who raise this many axolotl regret it .Idk your local laws on commercial animal sales or prices so cant advise on that. Survival rates depend on the care provided and the parents genetics. A healthy batch with perfect care should be 95%, with a few being unfit and a few culls one mistake can cause a mass die off.